Non-circular multicore fiber and method of manufacture

Abstract

A multicore fiber is provided. The multicore fiber includes a plurality of cores spaced apart from one another, and a cladding surrounding the plurality of cores and defining a substantially rectangular or cross-sectional shape having four corners. Each corner has a radius of curvature of less than 1000 microns. The multicore fiber may be drawn from a preform in a circular draw furnace in which a ratio of a maximum cross-sectional dimension of the preform to an inside diameter of the preform to an inside diameter of the draw furnace is greater than 0.60. The multicore fiber may have maxima reference surface.

What is claimed is: 
     
       1. A method of forming a multicore fiber comprising the steps of:
 forming a preform having a plurality of cores and cladding surrounding the cores, wherein the preform has a non-circular cross section with a plurality of corners and a maximum dimension across the cross section of the preform; 
 inserting the preform in a draw furnace having a substantially circular cross section such that a ratio of the maximum dimension of the preform to an inside diameter of the draw furnace is greater than 0.60; and 
 drawing a multicore fiber from the preform to achieve a reduction in cross-sectional size as the fiber is drawn while substantially maintaining a non-circular cross-sectional shape and the plurality of corners of the preform, wherein the multicore fiber is drawn at a draw speed of V draw  from a preform having maximum cross section dimension D p  in a draw furnace having peak temperature in Kelvin of T peak  and hot zone length of L draw  under conditions that result in non-dimensional draw parameter X=(L draw ×σ)/(V draw ×μ×D p ) to be less than 5×10 −6 ; wherein σ is the glass surface tension defined as σ (dynes/cm)=233.28+0.035×T peak  and μ is the glass viscosity defined as μ (Poise)=Exp[−13.738+(60604.7/T peak )]. 
 
     
     
       2. The method of  claim 1 , wherein the multicore fiber is drawn under conditions having non-dimensional draw parameter X less than 2×10 −6 . 
     
     
       3. The method of  claim 1 , wherein the multicore fiber is drawn under conditions having non-dimensional draw parameter X less than 1×10 −6 . 
     
     
       4. The method of  claim 1 , wherein the ratio of the maximum dimension of the preform to the inside diameter of the draw furnace is greater than 0.80. 
     
     
       5. The method of  claim 1 , wherein the ratio of the maximum dimension of the preform to the inside diameter of the draw furnace is greater than 0.90. 
     
     
       6. The method of  claim 1 , wherein the ratio of the maximum dimension of the preform to the inside diameter of the draw furnace is greater than 0.95. 
     
     
       7. The method of  claim 1 , wherein the fiber has a substantially rectangular cross-sectional shape having four corners, wherein each corner of the fiber has a radius of curvature of less than 1000 microns. 
     
     
       8. The method of  claim 7 , wherein each corner of the fiber has a radius of curvature of less than 500 microns. 
     
     
       9. The method of  claim 7 , wherein each corner of the fiber has a radius of curvature of less than 250 microns. 
     
     
       10. A method of forming a multicore fiber comprising the steps of:
 forming a preform having a plurality of cores and cladding surrounding the cores, wherein the preform has a non-circular cross section with a plurality of corners and a maximum dimension across the cross section of the preform; 
 inserting the preform in a draw furnace having a substantially circular cross section such that a ratio of the maximum dimension of the preform to an inside diameter of the draw furnace is greater than 0.70; and 
 drawing a multicore fiber from the preform to achieve a reduction in cross-sectional size as the fiber is drawn while substantially maintaining a non-circular cross-sectional shape and the plurality of corners of the preform. 
 
     
     
       11. A method of forming a multicore fiber comprising the steps of:
 forming a preform having a plurality of cores and cladding surrounding the cores, wherein the preform has a non-circular cross section with a plurality of corners and a maximum dimension across the cross section of the preform; 
 inserting the preform in a draw furnace having a substantially circular cross section such that a ratio of the maximum dimension of the preform to an inside diameter of the draw furnace is greater than 0.60; and 
 drawing a multicore fiber from the preform to achieve a reduction in cross-sectional size as the fiber is drawn while substantially maintaining a non-circular cross-sectional shape and the plurality of corners of the preform, wherein the step of forming the non-circular preform comprises: 
 forming a plurality of core canes each having a core surrounded by cladding; 
 processing each core cane to include at least one flat lateral surface; 
 aligning the flat lateral surface of adjoining canes; and 
 consolidating the aligned canes to form the preform. 
 
     
     
       12. The method of  claim 11 , wherein the step of processing each core cane comprises machining each core cane to include at least one flat lateral surface. 
     
     
       13. The method of  claim 11 , wherein the step of processing each core cane to include at least one flat lateral surface comprises processing each core cane to include four flat lateral surfaces. 
     
     
       14. A method of forming a multicore fiber comprising the steps of:
 forming a preform having a plurality of cores and cladding surrounding the cores, wherein the preform has a non-circular cross section with a plurality of corners and a maximum dimension across the cross section of the preform; 
 inserting the preform in a draw furnace having a substantially circular cross section such that a ratio of the maximum dimension of the preform to an inside diameter of the draw furnace is greater than 0.60; and 
 drawing a multicore fiber from the preform to achieve a reduction in cross-sectional size as the fiber is drawn while substantially maintaining a non-circular cross-sectional shape and the plurality of corners of the preform, wherein the fiber comprises an enlarged maxima member near each of the corners, and further comprises reduced maxima between adjacent corners so that the enlarged maxima members serve as alignment points.